Crystal amplifier



May 4, 1954 F. KOURY CRYSTAL AMPLIFIER Filed July 20, 1948 m E Wm M w AK \\\\\\X\\\\ 6 N 2 46 Hm Q n ATTORNEY Patented May 4, 1954 2,677,793CRYSTAL AMPLIFIER Frederic Koury, Somer Sylvania Electric Pro acorporation of Mass 13 Claims.

This invention relates to semi-conductors, and particularly tosemi-conducting crystals such as germanium, useful for electricalpurposes such as rectification, amplifiers and the like.

A point contact to such a crystal gives a rectifying action, and theaddition of one or more additional contacts close to the first willallow the device to be used as an amplifier. The setting of two contactsvery close to, but spaced from, each other introduce considerabledifficulty.

My invention facilitates the stable in adjustment.

A feature of the invention is the use of one or more concentric contactsbearing on the crystal. A further feature is a wire contact surroundedby an insulating layer which is in turn metallic layer. Severalseinsulation and metal may be used to produce a number of contacts.

Other objects, features and advantages of the invention will be apparentfrom the following specification taken with the accompanying drawing inwhich:

Figure 1 shows in section a cryst cording to the invention;

Figure 2 shows a cross-section through the contact Wire and itssurrounding layers; and

Figure 3 is a cross-section of a modification of the device in Figures 1and 2.

In Figure 1, the crystal which may be for example, of germanium with asuitable activating impurity such as tin, has a flat surface 2, on whichthe contacts 3, l rest.

The catwhisker or contact wire 5 may be of tungsten or other suitablemetal having an insulating coating 5 of a suitable material such ascellulose ester lacquer, synthetic resin or the like, in a thin filmfrom 0.00001" to 0.01" thick although for best results the coatingshould not ordinarily be much more than 0.001 thick. The metal coating lis applied over the insulating coating.

The insulating coating (1 be soaked in a solution or" stannous chlorideand hydrochloric acid for about 12 minutes. After thorough rinsing inwater it is then immersed in an ammonical solution of silver metals,about 8 cc. of 37% formaldehyde solution being added to each 100 cc. ofsilver nitrate solution. The coating 8 is then rinsed again in water,and a layer of silver plated thereon in a standard cyanide silverplating bath in the manner well known in the art. The thickness may be,for example, from 0.000001" to 0.1" as desired. A flash plate of nickelis added over the silver to facilitate soldering later to the lead-inwires 8, if desired.

The outer plated coating 1 may be spot-welded to a lead-in or contactwire 8, the central wire 5 being soldered to another lead-in wire 9.

a1 assembly acville, Mass, assignor to ducts Inc., Salem, Mass.

achusetts Application July 20, 1948, Serial No. 39,665

wire 5, 6, I may then be bent into an S-shape, preferably with the loops[9 and H opposite in direction, equal and having its longitudinal axisin a single plane. The straight end portions are preferably in line witheach other.

The end It of the wire 5, 6, l is immersed in an acetone solution to adepth of 0.005 inch to remove the plastic layer 6 away from the ends ofthe wire 5. Other solvents may be used if necessary or desirable for anyreason.

The ends 4 of wire 5 and layer I may be pointed electrolytically byimmersing the wire in a solution of sodium nitrite and sodium hydroxide,connecting the wire to the positive terminal of a direct current supply,of six volts, for example,

The composite and connecting the negative terminal to a nickel cathodein the solution. between about 20 and 50 amperes per square foot may bepassed between the electrodes for a few seconds to form a point on thewire end 3 and a sharp edge 4 or series of circumferential points aroundlayer 1.

The composite wire 5, 6, i may be cemented or otherwise passed throughand ailixed to an insulating piece I? and a germanium crystal brought upagainst the points or edges 3, t until the proper pressure is achievedfor the resistance desired. The back contact M, which is shown to be acontact of comparatively large area, may be attached to the germanium orother crystal by soldering or the like, and the metal or other support I5 used to hold the crystal in position in the cylinder 15, which may beof metal.

The resultant multi-electrode crystal may be used for many purposes. Forexample, the catwhisker 5 may be connected to a negative voltage, andthe layer 1 to a positive voltage with respect to back contact M, thesignal being impressed between layer 1 and contact I5, for example inseries with the positive voltage. The output current will then flow inthe circuit of catwhisker 5, but if desired, with the proper biasingvoltage, the catwhisker 5 may be used as the signal electrode and thelayer 7 as the output electrode. In one aspect this invention is aparticular form of device more broadly claimed in co-pendingapplication, Serial No. 39,367, filed July 17, 1948, by Orrick H. Big-gsand assigned to the assignee hereof and which is now abandoned.

As illustrated in Figure 3 and as mentioned above several sequentiallayers of insulation 6, B and metal I, 1 may be used to produce a numberof contacts concentrically about a wire 5, and these may be energizedand connected to the appropriate signal and output circuits, independence upon the circuit application.

What I claim is:

1. A semi-conductor unit comprising a semi- A current density ofconductive crystal, a conductor in substantially point-contact with saidcrystal, a contact of com-- paratively large area in engagement withsaid crystal, a coating of insulation extending along the longitudinalsurface of said conductor, and a metallic layer over said insulatingcoating and encircling said coating, the end of said layer being ofprogressively reduced thickness to provide a circumferential edgeencircling said conductor, said edge being in contact with said crystal.

2. A semi-conductor unit comprising a semiconductive crystal, aconductor in substantially point-contact with said crystal, a contact ofcornparatively large area in engagement with said crystal, a coating ofinsulation extending about said conductor along its length, and ametallic layer over said insulating coating and having a sharpened endportion in contact with said crystal, the composite structure includingsaid conductor, said coating, and said metallic layer being contoured soas to have a portion extending perpendicularly from the surface of saidcrystal, and having a laterally extending curved portion to afford aresilient engagement of the conductor and the metallic layer against thecrystal.

3. An electrical device comprising a body of semi-conductive material, aconductor in substantially point-contact with said body, a contact ofcomparatively large area in engagement with said body, a film ofinsulation about the lateral surface of said conductor, and a metallicsheath on said insulating layer and in endwise engagement with saidsemi-conductive body circuinferentially about the contact of saidconductor with said body, the separation of the conductor and themetallic sheath at the semi-conductive body being of the order of .001inch.

4. An electrical device including a semi-conductive body, a contact ofcomparatively large area in engagement therewith, and multipleconcentric conductors in endwise engagement with said body, saidconductors being mutually separated by insulating coating the thicknessof which is of the order of .001 inch.

5. An electrical device including a semi-conductive body, a contact ofcomparatively large area in engagement therewith, and multipleconcentrically arranged conductors in endwise engagement with said body,said conductors being separated by insulation, the composite concentricconductor and insulation structure being contoured to provide an arcuateresilient portion, and an additional portion extending perpendicularlyfrom the semi-conductive body.

6. lhe method of making a composite contact for a semi-conductor unit,including the steps of depositing a layer of metal on the exterior of alength of wire having a lateral coating of insulation, andelectrochemically sharpening the metal layer at its contact end.

7. lfhe method of making a composite contact for a semi-conductor unit,including the steps of depositing a layer of metal on the exterior of alength of wire having a lateral coating of insulation, dissolving theinsulation from a limited space at the end of the wire between the wireand the film, and electrochemically sharpening the metal film at itscontact end.

8. The method of making a composite contact for a semi-conductor unitincluding the steps of depositing a layer of metal on the exterior of alength of wire having a lateral coating of insulation and dissolving theinsulation from a limited space at the-end of the wire between the wireand the film.

9. A transistor, including a body of semiconductive material, a contactof comparatively large area on said body, and several sequentiallyconcentric conductors in sharp contact with said semiconductive body andseparated from each other by thin layers of insulation.

10. A transistor, including a body of semiconductive material, a firstconductor in substantially point-contact with said body, a contact ofcomparatively large area in engagement with said body, a thin layer ofinsulation about the lateral surface of said conductor, a secondconductor engaging said body and surrounding said insulation andminutely spaced from said first conductor by said insulation, a furtherlayer of insulation on said second conductor, and a further cylindricalcontact, in sequence, surrounding said further layer of insulation.

11. A transistor, including a semiconductive crystal, a base contact onsaid crystal, an insulated metal wire having one end in substantiallypoint-contact with said crystal, a first cylindrical contact concentricwith and encasing said wire but minutely insulated therefrom, and asecond contact concentrically about said first cylindrical contacts butminutely insulated therefrom, said cylindrical contacts being incircumferential contact with said crystal about said wire contact pointand permanently positioned in close proximity with one another.

12. In a multi-element concentric co axlal translating device, theelements comprising a semiconductive crystal, at base contact on saidcrystal, an insulated metal wire one end of which in point contact withsaid crystal, a plurality of concentric cylindrical metal contactscompletely surrounding said wire each being separated and insulated fromthe next larger by a thin layer of insulation on the outer surface ofthe next smaller in diameter, and each of said contacts in concentriccircumferential contact with said crystal about said contact point andpermanently in close proximity with adjacent circumferential contacts.

13. A semi-conductor unit comprising a semiconductive crystal, aconductor in su-*stantially point-contact with said crystal, a contactof comparatively large area in engagement with said crystal, a coatingof insulation extending along the longitudinal surface of saidconductor, and a metallic layer over said insulating coating andencircling said coating, the end of said layer being of progressivelyreduced thickness to provide a circumferential edge encircling saidconductor, said edge being in contact with said crystal, said insulatingcoating extending close to but spaced from the engagement of saidpoint-contact conductor with said crystal.

References Cited in the file of this patent UNITED STATES PATENTS

